We are attempting to generate mice lacking functional high affinity IgE receptor genes. These mice will help us to characterize the physiological function of the receptor and to further study the role of the receptor in allergy. We have cloned the alpha and beta chain genes from embryonic stem cells and have generated constructs which will be used to target the relevant genes by homologous recombination. When this is accomplished, we will attempt to produce mice in which the alpha or the beta have been knocked- out. If successful, we will be able to generate homozygotic mice in which both alleles will lack the functional genes encoding the alpha or beta gene.